In the known way, the rotating electric machine comprises two coaxial parts, i.e. a rotor and a stator surrounding the body of the rotor.
With reference to FIG. 1, an example of such a rotating electric machine referenced 100 is illustrated, in the case of an alternator with internal ventilation of the polyphase type for combustion engine automotive vehicles functioning in alternator mode. Naturally the alternator can also be reversible and consist of an alternator-starter also functioning in electric motor mode in particular to start the combustion engine of the vehicle as described in patent FR A 2 745 445 to ensure the propulsion of the automotive vehicle.
When machine 100 functions in alternator mode it converts mechanical energy to electrical energy like any alternator. When the machine functions in electric motor mode, particularly in starter mode to start the combustion engine of the vehicle, it converts electrical energy to mechanical energy.
This machine 100 primarily comprises a casing 1 and, inside the latter, a rotor 2 integral with a central shaft 3, known as rotor shaft, and a stator 50 of annular form, which surrounds rotor 2 with the presence of an air gap and which comprises a body 4 in the shape of a stack of steel sheets equipped with slots, for example of the half-closed type, for assembling a stator winding 5 forming on either side of body 4 of stator 50, at each axial end of the latter, a front winding head 51 and a rear winding head 53 which protrude axially.
This winding 5 for example comprises a set of three-phase coils in star or delta-connection, the outputs of which are connected to a rectifying bridge, partially visible in 52, comprising rectifying elements such as diodes or transistors of the MOSFET type, in particular if the machine consists of an alternator-starter.
Coils of winding 5 are obtained using a continuous, electrically conductive wire, covered with an electrically insulating layer, such as enamel, and assembled in the slots concerned of body 4 of stator 50 via slot insulators (not visible).
According to another alternative embodiment, winding 5 comprises two sets of three-phase coils to form a composite coil stator device, the coils being shifted by thirty electric degrees as described for example in patents US-A1-2002/0175589 and FR-A-2 784 248. In this case it is proposed that two rectifying bridges and all combinations of three-phase coils with star- and/or delta-connection are possible. Alternatively the winding of the stator is of the pentaphase type.
Generally the alternator is of the polyphase type and the bridge rectifiers in particular make it possible to rectify AC generated in the coils of stator 50 into DC, in particular to charge the battery of the automotive vehicle and to supply the loads and the electric consumers of the on-board power system of the automotive vehicle.
Rotor 2 of annular form is constructed in the example illustrated in the shape of a claw rotor, as described for example in patent US-A1-2002/0175589, comprising two polar wheels 7, 8 axially juxtaposed here and each exhibiting a transverse flange of annular form provided on its outer periphery of claws 9.
Each claw 9 comprises a root section of transversal orientation in the plane of the flange concerned. This root section is prolonged on its outer periphery by a tooth of broadly axial orientation with the presence of a chamfer between the tooth and the root section.
An annular air gap exists between the outer peripheral face of the teeth of claws 9 and the inner periphery of body 4 of stator 50.
The teeth overall are of trapezoidal or triangular form. The teeth of a polar wheel 7, 8 are directed axially towards the flange of the other polar wheel 8, 7, the tooth of a wheel 7, 8 penetrating in the space existing between two adjacent teeth of the other wheel 7, 8, so that the teeth of wheels 7, 8 overlap. For more precise details reference shall be made to patent EP 0515259.
A field winding 10 is axially arranged between the flanges of wheels 7, 8. It is supported by part of rotor 2 in the form of a cylindrical annular core coaxial to shaft 3. The core of FIG. 1 consists of two axially distinct sections, each of which is based on material associated with a polar wheel 7, 8. According to an alternative embodiment, not illustrated, the core consists of a single part and is distinct from polar wheels 7, 8 which are axially arranged on either side of the core.
Winding 10 is thus arranged in the space delineated radially by claws 9 of wheels 7, 8 and the central core.
Wheels 7, 8 and the core preferably consist of ferromagnetic material and are passed through in a coaxial way by the shaft of rotor 3, also made from ferromagnetic material. These wheels 7, 8 are integral with shaft 3. For this purpose, each wheel 7, 8 comprises a central boring which axially passes through the flange and prolongs the boring of the part of the core concerned. Shaft 3 exhibits knurled portions (not referenced) and is fixed by force in said borings of the core and wheels 7, 8, so that it cuts furrows by way of its knurled portions. Shaft 3 is thus integral and axially fixed with the wheels, a spacer, not referenced, being interposed between wheel 7 and a bearing 19 described below.
The axis of shaft 3 constitutes axis X of the machine. The wire of winding 10 is wound on a bracket made of electrically insulating material (not illustrated) mounted, preferably by force, on the outer periphery of the core.
When the field winding 10 is activated, i.e. electrically energized, wheels 7, 8 and the core, are magnetized and rotor 2 becomes an inductive rotor with magnetic poles being formed around claws 9 of wheels 7, 8.
This inductive rotor 2 creates an alternating current induced in stator 50 when shaft 3 rotates.
Shaft 3 of rotor 2 at its front end supports a movement transmission system 12, here a pulley 12 pertaining to a movement transmission device by means of at least one belt (not illustrated) between the alternator and the combustion engine of the automotive vehicle. This shaft at its rear end supports slip rings 13 connected by wired connections (not illustrated) on the ends of field winding 10 of rotor 2.
Alternatively pulley 12 is replaced by a gearbox and the transmission device has a chain and/or gears.
Brushes belong to a brush holder illustrated in a general way by reference symbol 14 and are designed to rub on slip rings 13, in order to supply winding 10 with electric current. Brush holder 14 is connected to a voltage regulator (not illustrated).
Here casing 1 in which rotor 2 and stator 50 are placed is in two parts, namely a front flange 16 adjacent to pulley 12 and a rear flange 17 supporting rectifying brush holders 14 and generally bridge(s) and the voltage regulator. Flanges 16, 17 of annular form, for example based on aluminium, are of hollow form and each centrally support a ball-bearing 19 and 20 respectively for rotatably mounting shaft 3 of rotor 2. The flanges are assembled together using ties or screws as visible for example on FIG. 1 of patent EP 0515 259 mentioned above. In other words, casing 1 of machine 100 comprises front flange 16, also known as front bearing, and rear flange 17, also known as rear bearing.
On FIG. 1, an elastic system in the shape of a stack of metal sheets is provided on the outer periphery of body 4 of the stator to filter vibrations, with a flat joint 40 in front and plugs 41 at the rear, flexible and heat-conductive resin being inserted between the front flange and the stator body to evacuate heat.
Alternatively no joints are proposed. In all cases the stator is supported in a fixed way by casing 1, while rotor 2 is centrally mounted for rotation by casing 1 via bearings 19, 20.
Alternatively the casing is in three parts, flanges 16, 17 being arranged on either side of a central part supporting the stator body. The flanges are assembled with the intermediate part for example by screwing.
The alternator also comprises means for its cooling. For this purpose, on FIG. 1, flanges 16, 17 are open to allow cooling of the alternator by air circulation and rotor 2 supports a fan intended to ensure this air circulation, at least on one of its axial ends. Here a first fan 23 is provided on the front face of rotor 2 and a second fan 24 on the rear face of rotor 12. Each fan 23, 24 is of annular form and equipped with a plurality of blades 26 and is fixed on the outer radial faces of the flanges of wheels 7, 8.
The fans are for example metal and obtained with their blades 26 by cutting and folding. Fans 23, 24 are for example of the centrifugal or helical-centrifugal type.
With reference to FIG. 1, the air is aspired through openings 60 of the front flange surrounding pulley 12 in front of the flange, then is mainly ejected in a centrifugal way by blades 26 and passes in the space between front winding head 51 and front flange 16 to cool the front winding head and finally to exit through openings 61 on the outer radial periphery of the front flange. Rear flange 17 also has a plurality of air intake and outlet openings.
On FIG. 1, brush holder 14 and the voltage regulator, integral with flange 17, are capped by a cover 70, integral with rear flange 17, being fixed here on the latter, in a way known, by click-and-ratchet work on pins 71 integral with the rear flange. This cover 70 also has air intake openings, not visible on FIG. 1.
FIG. 2 illustrates a claw rotor according to the prior art. It comprises a pair of overlapping wheels 7 and 8. Wheels 7 and 8 comprise claws 9. In an optional way rotor 2 comprises inter polar magnets 38. Rotor 2 shown on FIG. 2 comprises 8 pairs of poles.
Although this machine is satisfactory, it may be desirable to improve the latter particularly by attenuating the noise which it generates when in operation, driven by the combustion engine or in the case of an alternator-starter when it functions in motor mode.